Processes for preparing polyol fatty acid polyesters, including processes that utilize solvent-free transesterification reactions, have been described in U.S. Pat. No.: 3,963,699, Rizzi et al., issued Jun. 15, 1976; U.S. Pat. No. 4,517,360, Volpenhein, issued May 14, 1985; and U.S. Pat. No. 4,518,772, Volpenhein, issued May 21, 1985. Additional patents describing processes for preparing lower and higher esters of polyols include U.S. Pat. Nos.: U.S. Pat. No. 2,893,990, Hass et al., issued Jul. 7, 1959; U.S. Pat. No. 3,251,827, Schnell et al., issued May 17, 1966, which discloses that the particle size of the sugar should be kept small to avoid formation of higher esters; U.S. Pat. No. 3,558,597, Brachel et al., issued Jan. 26, 1971; U.S. Pat. No. 3,644,333, Osipow et al., issued Feb. 22, 1972; U.S. Pat. No. 3,792,041, Yamagishi et al., issued Feb. 12, 1974, which discloses making a solution of sucrose and fatty acid soap in water and adding the fatty acid ester and catalyst before elevating the temperature to drive off the water, U.S. Pat. No. 4,032,702, James, issued Jun. 28, 1977, which discloses using lower esters of sucrose as emulsifiers in the preparation of lower esters and the use of soap as a catalyst for such reactions; U.S. Pat. No. 4,298,730, Galleymore et al., issued Nov. 3, 1981, which also discloses the use of soap as an emulsifier and catalyst; U.S. Pat. No. 4,334,061, Bossier et al., issued Jun. 8, 1982, which discloses the use of a water washing step to purify the polyol polyester and incidentally discloses the use of inert gas sparging to remove lower alcohol from the reaction between sucrose and lower alkyl ester of fatty acid to speed the reaction and the removal of unreacted sucrose from an initial stage of a batch reaction for no indicated reason; and U.S. Pat. No. 4,877,871, Klemann et al., issued Oct. 31, 1989.
Many of the above patents teach processes that use a solvent to assist in the formation of a homogeneous reaction mixture. However, the presence of the solvent is not desirable since it must then be removed. Also, many of the above processes primarily relate to the preparation of lower esters, containing one or two ester groups, that are desirable for use as surfactants. The present process primarily relates to an improved and highly effective method of preparing of polyol polyesters that have high degrees of esterification, preferably polyesters that are more than about 50% esterified, i.e., at least about 50% of the total number of available hydroxy groups on the polyol are esterified with a fatty acyl radical.
The presence of unreacted polyol in stage two has been surprisingly found to be a key detriment to the reaction rate and final conversion of the polyol to greater than 85% degree of esterification. The removal of essentially all of the polyol (sucrose) before stage 2 greatly facilitates preparation of octa esters. In order to have a better commercial process for preparing highly esterified polyols, it is desirable to have a fast continuous process.